1. Field of the Invention
The present invention relates to a semiconductor device including a semi-conductive oxide and a manufacturing method thereof.
In this specification, a semiconductor device generally means a device which can function by utilizing semiconductor characteristics, and an electro-optical device, a semiconductor circuit, and electronic devices are all semiconductor devices.
2. Description of the Related Art
In recent years, a technique for forming transistors using a semiconductor thin film (with a thickness of approximately several tens to several hundreds of nanometers) formed over a substrate having an insulating surface has attracted attention. Transistors are applied to a wide range of electronic devices like integrated circuits and electro-optical devices, and transistors that are to be used as switching elements in image display devices, in particular, has been developed.
Some oxides have semiconductor characteristics. Examples of such oxides having semiconductor characteristics are a tungsten oxide, a tin oxide, and an indium-gallium-zinc-based oxide (In—Ga—Zn-based oxide), and a thin film transistor in which such an oxide having semiconductor characteristics is used for a channel formation region is known (see Patent Documents 1 and 2). Further, in particular, properties of an In—Ga—Zn-based oxide also have been researched (Non-Patent Document 1).